The present invention relates to torsion spring suspensions, and particularly to axle suspensions for wheeled frames such as are used on trailers and other vehicles, and the like, and to a torsion spring suspension assembly having features facilitating shipment, storage, installation, and improved operation.
Solid axle suspensions incorporating leaf springs and the like are often used on trailers and other such vehicles since they are relatively inexpensive to manufacture, and relatively easy to install. Further, the way in which a trailer frame is supported on such an axle suspension tends to distribute stress to the trailer frame in a balanced and desirable manner. However, solid axle suspensions are expensive to ship since they cannot be collapsed in size for shipment. Further, a different size of solid axle must be stocked for each different trailer width, and thus large inventories and correspondingly large storage areas must be maintained.
Torsion spring suspensions offer an attractive alternative to leaf spring suspensions and solid axles since torsion spring suspensions typically offer improved handling, a smoother ride, and a lower center of gravity. Also, torsion spring assemblies do not include a long solid axle and thus less inventory is required to cover various different frame widths. However, torsion spring assemblies tend to be more costly due to the specialized parts and equipment required to manufacture them. Further, the specialized parts and equipment can lead to product inconsistency and warranty problems.
Some torsion spring assemblies utilize rubber as the torsional stress absorber. However, rubber is sensitive to temperature changes, and hence, the torsion spring assembly load ratings and spring rates of such torsion spring assemblies may vary significantly with temperature. Further, such rubber suspension can be difficult to assemble consistently since the rubber components must typically be frozen first to reduce their size by contraction. Still further, once the rubber is assembled into the torsion spring assembly, clips and brackets cannot be welded to the outer cartridge or axle tube of the assembly and the latter cannot be mounted by welding since high weld temperatures will damage the rubber. Also, such axle assemblies tend to be very heavy due to the extensive amount of high-durometer rubber they use, and thus can be expensive to ship.
Still other torsion spring assemblies utilize metal or other torsion bars instead of rubber. These assemblies typically require use of a motion limiter to control over-rotation or over-torquing of the torsion springs. However, present motion limiters transmit the over-stress condition to the torsion spring axle tube in a way that causes the axle tube to prematurely fail. For example, the motion limiter is often a polygonally shaped plate that rotates in the axle tube, pressing outwardly on the flat sides of the axle tube during over-torquing of the torsion spring assembly and potentially causing the cross-sectional profile of the axle tube to plastically deform. When this happens, the limiter may well fail, typically with disastrous consequences, and a completely new axle, or at least axle tube, is required to repair the suspension. Usually, when the axle tube is seriously damaged, substantially all of the major parts must be discarded and an entire new torsion spring assembly installed.
Thus, there is a need for a suspension assembly having the advantages of solid axles and also of torsion spring assemblies, but which is more easily shipped, stored, and installed. Further, there is a need for a suspension assembly which is adaptable to fit differently sized frames. Also, there is a need for a torsion spring subassembly that requires less specialized parts and less specialized machinery to assemble same, and which distributes stress in a manner reducing the tendency to plastically deform parts during overload and over-rotation conditions. Furthermore, there is a pronounced need for a torsion spring subassembly having a safe and completely reliable motion limiter which will operate repeatedly without damaging the assembly or impairing its ability to function properly.